Rule2022-26435
Special Conditions: Airbus Model A321neoXLR Airplane; Passenger Protection From External Fire
Primary source
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Published
December 6, 2022
Effective
January 5, 2023
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
These special conditions are issued for the Airbus Model A321neoXLR airplane. This airplane will have a novel or unusual design feature when compared to the technology envisaged by the airworthiness standards for transport category airplanes. This design feature is an integral rear center tank (RCT). The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. These special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.
Full Text
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<title>Federal Register, Volume 87 Issue 233 (Tuesday, December 6, 2022)</title>
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[Federal Register Volume 87, Number 233 (Tuesday, December 6, 2022)]
[Rules and Regulations]
[Pages 74503-74505]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2022-26435]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. FAA-2021-0891; Special Condition No. 25-825-SC]
Special Conditions: Airbus Model A321neoXLR Airplane; Passenger
Protection From External Fire
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for the Airbus Model
A321neoXLR airplane. This airplane will have a novel or unusual design
feature when compared to the technology envisaged by the airworthiness
standards for transport category airplanes. This design feature is an
integral rear center tank (RCT). The applicable airworthiness
regulations do not contain adequate or appropriate safety standards for
this design feature. These special conditions contain the additional
safety standards that the Administrator considers necessary to
establish a level of safety equivalent to that established by the
existing airworthiness standards.
DATES: Effective January 5, 2023.
FOR FURTHER INFORMATION CONTACT: Shannon Lennon, Human Machine
Interface, AIR-626, Technical Innovation Policy Branch, Policy and
Innovation Division, Aircraft Certification Service, Federal Aviation
Administration, 2200 South 216th Street, Des Moines, Washington 98198;
telephone and fax 206-231-3209; email <a href="/cdn-cgi/l/email-protection#9eedf6fff0f0f1f0b0f2fbf0f0f1f0def8ffffb0f9f1e8"><span class="__cf_email__" data-cfemail="23504b424d4d4c4d0d4f464d4d4c4d634542420d444c55">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION:
Background
On September 16, 2019, Airbus applied for an amendment to Type
Certificate No. A28NM to include the new Model A321neoXLR airplane. The
Model A321neoXLR airplane, which is a derivative of the Model
A321neoACF airplane currently approved under Type
[[Page 74504]]
Certificate No. A28NM, is a twin-engine transport category aircraft
that seats 244 passengers and has a maximum takeoff weight of 202,000
lbs.
Type Certification Basis
Under the provisions of title 14, Code of Federal Regulations (14
CFR) 21.101, Airbus must show that the Model A321neoXLR airplane meets
the applicable provisions of the regulations listed in Type Certificate
No. A28NM, or the applicable regulations in effect on the date of
application for the change, except for earlier amendments as agreed
upon by the FAA.
If the Administrator finds that the applicable airworthiness
regulations (e.g., 14 CFR part 25) do not contain adequate or
appropriate safety standards for the Airbus Model A321neoXLR airplane
because of a novel or unusual design feature, special conditions are
prescribed under the provisions of Sec. 21.16.
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same novel or
unusual design feature, or should any other model already included on
the same type certificate be modified to incorporate the same novel or
unusual design feature, these special conditions would also apply to
the other model under Sec. 21.101.
In addition to the applicable airworthiness regulations and special
conditions, the Airbus Model A321neoXLR airplane must comply with the
fuel vent and exhaust emission requirements of 14 CFR part 34 and the
noise certification requirements of 14 CFR part 36.
The FAA issues special conditions, as defined in 14 CFR 11.19, in
accordance with Sec. 11.38, and they become part of the type
certification basis under Sec. 21.101.
Novel or Unusual Design Feature
The Airbus Model A321neoXLR airplane will incorporate the following
novel or unusual design feature:
An integral RCT.
Discussion
The Airbus Model A321neoXLR incorporates an integral RCT. This tank
is a ``center'' fuel tank, in that it is located in the airplane
fuselage rather than in its wings. The tank is a ``rear'' tank, in that
it is located aft of the wheel bay; it will be in an area of the lower
fuselage that partially replaces the aft cargo compartment of the
airplane from which this model is derived. The top of the tank will be
directly below the floor of the passenger cabin. The fuel tank will be
``integral'' to the airplane, in that its walls will be part of the
airplane structure. The exterior skin of the airplane fuselage will
constitute part of the walls of the fuel tank, and these areas will
lack the thermal/acoustic insulation that usually lines the exterior
skin of an airplane fuselage.
This design was not envisaged by the FAA's regulatory requirements
for insulation installations on transport category airplanes. 14 CFR
25.856(b) requires all thermal/acoustic insulation in the lower half of
the airplane fuselage and their installation to comply with the flame
penetration resistance test of appendix F, part VII. The FAA adopted
Sec. 25.856(b) to raise the level of post-crash fire safety on
transport category airplanes. Part VII of appendix F to part 25
requires a stringent test method for all thermal/acoustic insulation
proposed for installation in the lower half of the fuselage. The FAA's
intent in imposing this requirement was to ensure that this insulation
provides an additional barrier between the occupants and an external
post-crash fire, especially a fire resulting from a pool of spilled
aviation fuel.\1\ This barrier extends the time available for
evacuation.
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\1\ See pg. 2 of FAA Advisory Circular 25.856-2A, Installation
of Thermal/Acoustic Insulation for Burnthrough Protection.
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While the rule applies to the thermal/acoustic insulation that an
applicant proposes as part of their design, it does not require
applicants to install such insulation. Since the fuselage skins of the
lower half of transport category airplanes are generally insulated, and
were at the time these standards were developed, the FAA considered
this approach to be sufficient to ensure safety. The rule also noted,
however, that if applicants began to propose designs that omitted this
thermal/acoustic insulation, the FAA would revisit the need for a
specific fuselage burnthrough standard.\2\
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\2\ Improved Flammability Standards for Thermal/Acoustic
Insulation Materials Used In Transport Category Airplanes, 68 FR
45046, 45049 (Jul. 31, 2003).
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Thus, since this design will lack thermal/acoustic insulation under
the fuselage skin in the area of the fuel tank, current FAA regulations
do not ensure that it will provide a continuous flame penetration
(burnthrough) resistant barrier between the passengers and an external
fire, nor that it will provide enough protection, against an external
post-crash fire, to allow time for passengers to evacuate.
According to Airbus, its design does not allow for compliant
thermal/acoustic insulation to be placed beneath the cabin floor. This
large volume of unheated liquid (fuel), directly below the floor of the
passenger cabin, would, without mitigation, create a 'cold feet' effect
for the passengers above it. Therefore, Airbus will install insulation
panels between the fuel tank and the cabin floor, for comfort reasons.
These insulation panels would normally be required to meet Sec.
25.856(b). However, Airbus states that it is technically not feasible
to install thermal/acoustic insulation that complies with Sec.
25.856(b), due to the lack of space in this area and the need to keep
nearby decompression panels free of blockages and ensure adequate
ventilation.
Special conditions are needed to address the assumption in the
FAA's current flammability standards that proposed airplane designs
would include thermal/acoustic insulation in the lower fuselage, and to
ensure that this proposed design does not reduce the time available for
passenger evacuation in the case of a post-crash external fire.
Specifically, the FAA will require that the lower half of the airplane
fuselage, spanning the longitudinal area of the tank, be resistant to
fire penetration. ``Resistant to fire penetration'' will, for this
special condition, mean that this area provides fire penetration
resistance equivalent to the resistance which would be provided if the
fuselage were lined with thermal/acoustic insulation that meets the
flame penetration resistance test requirements of part VII of appendix
F of part 25. The applicant's method of compliance may, but is not
required to, be based upon any inherent flame penetration resistance
capability provided by the construction of the fuel tank and/or other
surrounding features.
These special conditions contain the additional safety standards
that the Administrator considers necessary to establish a level of
safety equivalent to that established by the existing airworthiness
standards.
Discussion of Comments
The FAA issued Notice of Proposed Special Conditions No. 25-21-04-
SC for the Model A321neoXLR airplane, which was published in the
Federal Register on April 6, 2022 (87 FR 19811). The FAA received four
comments from the Boeing Company (Boeing).
Comment Summary: Boeing requested that the discussion section of
these special conditions describe the RCT as an ``auxiliary,'' rather
than ``center,'' fuel tank because the airplane also has a ``center''
wing (main) tank, and because, as described by Advisory Circular (AC)
25-8, Auxiliary Fuel
[[Page 74505]]
Systems Installations, the RCT would be connected to the main tank with
a fuel feed line. Boeing also requested that the discussion section
describe the tank as an ``aft'' fuel tank rather than a ``rear'' tank,
because it will be aft of the wheel bay.
FAA Response: No change to the terms used to describe the RCT in
these special conditions is necessary. The existing terms are accurate,
consistent with the applicant's nomenclature, and adequate for their
purpose.
Comment Summary: Boeing requested that the discussion section of
these special conditions acknowledge that AC 25.856-2A \3\ provides
guidance for center wing tank designs. Boeing further requested that
the discussion, according to guidance provided in that AC for the wing
box area, also indicate that insulation panels installed above a fuel
tank are not required to meet Sec. 25.856(b).
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\3\ See pg. 2 of FAA Advisory Circular 25.856-2A, Installation
of Thermal/Acoustic Insulation for Burnthrough Protection.
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FAA Response: The discussion for these special conditions
acknowledges that Sec. 25.856(b) does not adequately address designs
like the RCT of the A321neoXLR. This aircraft presents a novel fuselage
design that does not incorporate thermal/acoustic insulation in areas
where the RCT is integral to the fuselage, nor does it include thermal/
acoustic insulation above the RCT that will meet Sec. 25.856(b). This
design presents a fire penetration resistance (burnthrough)
vulnerability that is addressed by these special conditions. The same
vulnerability does not exist with transport airplane wing box
construction due to that structure's significant mass, and large
surface area that dissipates heat. Therefore, adding insulation over
the wingbox, would not contribute to its fire penetration resistance.
14 CFR 25.856(b) excepts the installation of insulation in locations
where it would not contribute to fire penetration resistance. However,
the wing box example in AC 25.856-2A only addresses the FAA's
assessment of the wing box area in consideration of thermal/acoustic
insulation installations that would not contribute to fire penetration
resistance. It does not suggest that all center fuel tanks do not
necessitate the installation of thermal/acoustic insulation that meets
Sec. 25.856(b). For this reason, the FAA declines to change the
discussion section of these special conditions.
Comment Summary: Boeing requested that the special conditions
require the RCT fire penetration resistance capability to either be
equivalent to the capability provided by the wing box area or meet the
requirements of 14 CFR 25.963(e)(2). Boeing's rationale was that the
FAA's proposed standard of fire penetration resistance equivalent to
that of a fuselage lined with thermal/acoustic insulation that meets
the flame penetration resistance test requirements of part VII of
appendix F, does not address hazards associated with fuel tanks and is
not applicable to the wing box area.
FAA Response: These special conditions are intended to ensure that
the existing RCT area fuselage design establishes the same level of
safety as would 14 CFR 25.856(b). When thermal/acoustic insulation is
installed, either along the fuselage skin or under the passenger cabin
floor, it should be fire penetration resistant and delay the onset of
fire into the passenger cabin. These special conditions are not
intended to ensure the RCT is constructed to provide a fire penetration
resistance capability that is similar to that of the wing box area. It
is also unnecessary to require that the RCT meet rules such as 14 CFR
25.963(e)(2), which provides standards for fuel tank access covers.
The special conditions are adopted as proposed.
Applicability
As discussed above, these special conditions are applicable to the
Airbus Model A321neoXLR airplane. Should Airbus apply at a later date
for a change to the type certificate to include another model
incorporating the same novel or unusual design feature, these special
conditions would apply to that model as well.
Conclusion
This action affects only a certain novel or unusual design feature
on one model of airplane. It is not a rule of general applicability.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
Authority Citation
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(f), 106(g), 40113, 44701, 44702, 44704.
The Special Conditions
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special conditions are issued as part of
the type certification basis for Airbus Model A321neoXLR airplanes.
Passenger Protection From External Fire
The lower half of the fuselage, spanning the longitudinal location
of the rear center fuel tank, must be resistant to fire penetration.
Issued in Kansas City, Missouri, on November 30, 2022.
Patrick R. Mullen,
Manager, Technical Innovation Policy Branch, Policy and Innovation
Division, Aircraft Certification Service.
[FR Doc. 2022-26435 Filed 12-5-22; 8:45 am]
BILLING CODE 4910-13-P
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